A patent document 1 (i.e., Japanese Patent Laid-Open No. 4280648) discloses a projection type display device which displays an image by projecting an image light onto a predetermined region of a vehicle compartment. The above-described predetermined region is a surface of a front pillar on a side of the vehicle compartment. The projection type display device of the patent document 1 projects an image light onto the surface of the front pillar to display an image on such surface.
The window which constitutes a part of a vehicle compartment provides a field of view for the vehicle occupant. The transparency of the window provides a view of an outside of the vehicle through the window and does not obstruct or obscure the view of the occupant. Further, in addition to having a view of the outside through the window, it is also desired to display an image on the same window.
However, the projection type display device of the patent document 1 mentioned above cannot be used to provide such a display function because the image cannot be displayed on a transparent window. In contrast, in the patent document 1, the surface of the front pillar upon which the projection type display device projects the image light is opaque.